1. Field of the Invention
The invention relates to electric circuit breakers, and more particularly to molded case circuit breakers having a flexible braid in the current path.
2. Description of the Prior Art
Electric circuit breakers are known, having electromagnetic tripping means which cause instantaneous tripping of the breaker when a current flows through the breaker which is in excess of a predetermined threshold current. Such a threshold current may, for example, be between three and five times the rated normal operating current for the breaker. Electric circuit breakers are also known, having tripping means in the form of bimetallic members which are resistively heated by the current flowing through the breaker and which trip the breaker when a current flows through the breaker which is in excess of a predetermined threshold current. It is also known to use a combination of electromagnetic tripping means and bimetallic tripping means.
Tripping arrangements for circuit breakers usually use a movable latch member for holding an actuating member of a switching arrangement of the breaker until the breaker is tripped by moving the latch member so as to unlatch the actuating member. The actuating member is then free to move under the action of spring means contained in the switching arrangement, so that the previously closed contacts of the switching arrangement are rapidly opened.
Irrespective of whether the tripping arrangement uses electromagnetic tripping means, or bimetallic tripping means, or both, the electric current flowing through the breaker passes through the tripping arrangement. Usually, the current is conducted to the tripping arrangement from a movable contact of the breaker, by way of a conductive flexible metallic braid one end of which is connected to a movable-contact-carrying element, and the other end of which is connected to the electromagnet or bimetallic member of the tripping arrangement.
In the confined interior space of small circuit breakers, it is easy for the conductive braid to touch the latch member, which itself may touch other current-carrying parts of the tripping arrangement, thus establishing an undesired parallel current flow path. For example, when electromagnetic tripping is used, the said other end of the braid is connected to one terminal of a tripping electromagnet. If, undesirably, the braid were also to touch a current carrying part of the tripping arrangement at a place subsequent to the other terminal of the electromagnet, either directly, or by way of touching the latch member, a parallel current flow path would be established which would shunt the electromagnet and thus impair its action.
In small circuit breakers, the above-mentioned actuating member is usually part of a cradle member which is linked to the movable-contact-carrying element of the breaker by way of an overcenter spring. There thus exists the danger that a parallel current flow path can be established from the movable-contact-carrying element through the overcenter spring, the cradle member and the latch member, to the bimetallic or electromagnetic tripping arrangement, rather than solely through the metallic braid.